1. Field of the Invention
The invention relates to a split cage for a rolling bearing, in which a plurality of cage segments is annularly arranged.
2. Description of the Related Art
In conventional horizontal axis propeller type wind power generation apparatuses, rolling bearings are used to rotatably support a main shaft to which blades are attached. In recent years, since the sizes of the wind power generation apparatuses are increased, the diameter of the main shaft may exceed several meters. In order to support such a large-sized main shaft, the size of the rolling bearing is also increased. A cage formed of synthetic resin may be used for such a large-sized rolling bearing. The synthetic resin cage is advantageous over a metallic cage assembled by welding in that the synthetic resin cage is light in weight and a sufficient accuracy of the synthetic resin cage is easily achieved. However, it is not easy to mold a synthetic resin cage with a large diameter as an integral unit by injection molding. Therefore, a split cage formed of circumferentially divided pieces is used (e.g., see EP Patent No. 2264325 A1). In the split cage, a plurality of cage segments is annularly arranged.
FIG. 5 is a perspective view of a main portion of an example of a conventional cage segment. FIG. 6 is a sectional view of a main portion of a tapered roller bearing in which conventional cage segments are used. The cage segment 100 has a pair of first and second rim portions 101 and 102, and a plurality of bar portions 103 extending from the first rim portion 101 to the second rim portion 102. The first and second rim portions 101 and 102 are spaced from each other by a predetermined interval and face each other. In this cage segment 100, spaces, each of which is surrounded by the bar portions 103 adjacent to each other and the first and second rim portions 101 and 102, are formed as pockets 104 that house tapered rollers 113 (see FIG. 6) that are provided as rolling elements. The cage segment 100 is a synthetic resin cage molded by injection molding.
In the tapered roller bearing 110, a plurality of tapered rollers 113 is arranged between an outer ring 111 and an inner ring 112. The tapered rollers 113 are held by a split cage 120 that is formed of the cage segments 100. A raceway surface 112a on which the tapered rollers 113 roll is formed on an outer periphery of the inner ring 112. On two opposite sides of the raceway surface 112a, there are provided a large rib portion 112b and a small rib portion 112c that contact end surfaces of each tapered roller 113.
The tapered roller bearing 110 is assembled by, for example, arranging the cage segments 100 annularly along the outer periphery of the inner ring 112, sequentially inserting the tapered rollers 113 into the pockets 104 of the cage segments 100 and then fitting the outer ring 111 so that the outer periphery of the outer ring 111 contacts the tapered rollers 113.
In the tapered roller bearing 110 as described above, it is preferable that the number of tapered rollers 113 be as large as possible in order to secure a sufficient loading capacity of the bearing. Thus, the size of each bar portion 103 of each cage segment 100 in the circumferential direction is inevitably made small. If the thickness of each bar portion 103 is reduced, the sectional areas of the connecting portions between the bar portions 103 and the first and second rim portions 101 and 102 are also reduced. As a result, there is a possibility that the cage segment 100 may be impaired due to the reduction of the strength of the connection portions.